This invention relates to a method and system that reduces the average current consumption in a duty-cycled radio frequency (RF) receiver. Specifically, an RF receiver stabilization time is adjusted based on temperature measurements of the RF receiver operational environment.
RF systems typically include a transmitter that transmits a signal and an RF receiver that receives and responds to the signal from the transmitter. One example of such a system is in a remote keyless entry (RKE) system for a vehicle. A transmitter in a key fob transmits a signal to a receiver in the vehicle to unlock the vehicle doors.
These RKE systems are periodically placed in an active mode even when the vehicle is parked or is otherwise in a non-operational mode. The RF receiver is periodically activated to look for input data from the transmitter. A vehicle battery traditionally provides the power for the RF receiver. Each time the RF receiver is activated, the receiver must remain on until a receiver stabilization time has been achieved. The receiver stabilization time unique to each different type of RF receiver and is defined as the length of time needed to guarantee a valid output response from the RF receiver.
Typically, RF receivers have a longer stabilization time at lower temperatures. Current RF systems must wait for the worst case stabilization time for the RF receiver at all temperatures. For example, if a stabilization time of 6 milliseconds is required at lower temperatures, then the RF receiver remains on during an activation interval for 6 milliseconds at all temperatures. This results in a higher average current consumption over time, which in turn can drain the vehicle battery.
Thus, it is desirable to have a method and system that can reduce the average current consumption for an RF receiver in a duty-cycled application, as well as overcoming the other above-mentioned deficiencies with the prior art.
The system and method for reducing average current consumption in an RF system utilizes temperature sensing to adjust stabilization time. The stabilization time is defined as a period of time needed to produce a valid output response signal. The RF system includes a RF receiver that has a predetermined base RF receiver stabilization time. At least one temperature of a RF receiver operational environment is measured and the base RF receiver stabilization time is adjusted based on the measured temperature.
In one disclosed embodiment, the RF system is used in a remote keyless entry system in a vehicle. A transmitter is located in a key fob and a RF receiver is located within the vehicle. The RF receiver is periodically activated at a predetermined activation interval to search for input data. The temperature of the RF receiver operational environment is measured by at least one temperature sensor and the base RF receiver stabilization time is adjusted based on the temperature data to define an adjusted RF receiver stabilization time. The temperature that is measured can be either an external temperature, i.e. the temperature outside the vehicle, or an internal temperature, i.e. the temperature inside the vehicle.
In one disclosed embodiment, the adjusted RF receiver stabilization time is greater than or equal to the base RF receiver stabilization time if the temperature is below a predetermined limit and the adjusted RF receiver stabilization time is less than the base RF receiver stabilization time if the temperature is above a predetermined limit.
Preferably, at least one temperature of the operational environment is measured during each of the predetermined activation intervals and a control unit adjusts the base RF receiver stabilization time during each activation interval accordingly. The RF receiver includes a maximum current consumption average based on a predetermined maximum constant RF receiver stabilization time for all temperatures. A discrete adjusted RF receiver stabilization time is thus determined for each of the activation intervals. A measured average current consumption is determined by combining a plurality of the discrete adjusted RF receiver stabilization times compiled over time. The measured average current consumption is thus maintained at a current level below the maximum current consumption average as a result of adjustments made in response to the temperature measurements.
The subject system and method reduces the overall current consumption for an RF receiver in a duty-cycled application, which in turn reduces unnecessary drain on a power source. These and other features of the present invention can be best understood from the following specifications and drawings, the following of which is a brief description.